Signaling of random access preamble parameters in wireless networks

ABSTRACT

User equipment (UE)-initiated accesses within a cellular network are optimized to account for cell size and to reduce signaling overhead. A fixed set of preamble parameter configurations for use across a complete range of cell sizes within the cellular network is established and stored within each UE. A UE located in a given cell receives a configuration number transmitted from a nodeB serving the cell, the configuration number being indicative of a size of the cell. The UE selects a preamble parameter configuration from the fixed set of preamble parameter configurations in response to the received configuration number and then transmits a preamble from the UE to the nodeB using the preamble parameter configuration indicated by the configuration number.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of patent application Ser. No.15/804,967, filed Nov. 6, 2017, which is a continuation of patentapplication Ser. No. 15/167,515, filed May 27, 2016, (now U.S. Pat. No.9,814,066) which is a continuation of patent application Ser. No.11/970,239 filed Jan. 7, 2008, (now U.S. Pat. No. 9,357,564) whichclaims the benefit of Provisional Application No. 61/017,542 filed onDec. 29, 2007, entitled “Signaling of Random Access Preamble Parametersin Wireless Network,” and Provisional Application No. 60/944,913 filedon Jun. 19, 2007 entitled “Optimization of Random Access PreambleParameters Signaling in Wireless Networks” the content of all of whichare herein incorporated by reference in its entirety.

FIELD OF THE INVENTION

This invention generally relates to wireless cellular communication, andin particular to a non-synchronous request channel for use in orthogonaland single carrier frequency division multiple access (OFDMA) (SC-FDMA)systems.

BACKGROUND OF THE INVENTION

The Global System for Mobile Communications (GSM: originally from GroupeSpécial Mobile) is currently the most popular standard for mobile phonesin the world and is referred to as a 2G (second generation) system.Universal Mobile Telecommunications System (UMTS) is one of thethird-generation (3G) mobile phone technologies. Currently, the mostcommon form uses W-CDMA (Wideband Code Division Multiple Access) as theunderlying air interface. W-CDMA is the higher speed transmissionprotocol designed as a replacement for the aging 2G GSM networksdeployed worldwide. More technically, W-CDMA is a widebandspread-spectrum mobile air interface that utilizes the direct sequenceCode Division Multiple Access signaling method (or CDMA) to achievehigher speeds and support more users compared to the older TDMA (TimeDivision Multiple Access) signaling method of GSM networks.

Orthogonal Frequency Division Multiple Access (OFDMA) is a multi-userversion of the popular Orthogonal Frequency-Division Multiplexing (OFDM)digital modulation scheme. Multiple access is achieved in OFDMA byassigning subsets of sub-carriers to individual users. This allowssimultaneous low data rate transmission from several users. Based onfeedback information about the channel conditions, adaptiveuser-to-sub-carrier assignment can be achieved. If the assignment isdone sufficiently fast, this further improves the OFDM robustness tofast fading and narrow-band co-channel interference, and makes itpossible to achieve even better system spectral efficiency. Differentnumber of sub-carriers can be assigned to different users, in view tosupport differentiated Quality of Service (QoS), i.e. to control thedata rate and error probability individually for each user. OFDMA isused in the mobility mode of IEEE 802.16 WirelessMAN Air Interfacestandard, commonly referred to as WiMAX. OFDMA is currently a workingassumption in 3GPP Long Term Evolution (LTE) downlink. Also, OFDMA isthe candidate access method for the IEEE 802.22 “Wireless Regional AreaNetworks”.

NodeB is a term used in UMTS to denote the BTS (base transceiverstation). In contrast with GSM base stations, NodeB uses WCDMA or OFDMAas air transport technology, depending on the type of network. As in allcellular systems, such as UMTS and GSM, NodeB contains radio frequencytransmitter(s) and the receiver(s) used to communicate directly with themobiles, which move freely around it. In this type of cellular networksthe mobiles cannot communicate directly with each other but have tocommunicate with the BTSs.

Traditionally, the NodeBs have minimum functionality, and are controlledby an RNC (Radio Network Controller). However, this is changing with theemergence of High Speed Downlink Packet Access (HSDPA), where some logic(e.g. retransmission) is handled on the NodeB for lower response timesand in 3GPP long term evolution (LTE) wireless networks (a.k.a.E-UTRA—Evolved Universal Terrestrial Radio Access Network) almost allthe RNC functionalities have moved to the NodeB. A NodeB is generally afixed station and may be called a base transceiver system (BTS), anaccess point, a base station, or various other names. As the network hasevolved, a NodeB is also referred to as an “evolved NodeB” (eNB).

In WCDMA and OFDMA the cell's size is not constant (a phenomenon knownas “cell breathing”). This requires a careful planning in 3G (UMTS)networks. Power requirements on NodeBs and UE (user equipment) aretypically lower than in GSM.

A NodeB can serve several cells, also called sectors, depending on theconfiguration and type of antenna. Common configuration include omnicell (360°), 3 sectors) (3×120° or 6 sectors (3 sectors 120° wideoverlapping with 3 sectors of different frequency).

High-Speed Packet Access (HSPA) is a collection of mobile telephonyprotocols that extend and improve the performance of existing UMTSprotocols. Two standards HSDPA and HSUPA have been established. HighSpeed Uplink Packet Access (HSUPA) is a packet-based data service ofUniversal Mobile Telecommunication Services (UMTS) with typical datatransmission capacity of a few megabits per second, thus enabling theuse of symmetric high-speed data services, such as video conferencing,between user equipment and a network infrastructure.

An uplink data transfer mechanism in the HSUPA is provided by physicalHSUPA channels, such as an Enhanced Dedicated Physical Data Channel(E-DPDCH), implemented on top of the uplink physical data channels suchas a Dedicated Physical Control Channel (DPCCH) and a Dedicated PhysicalData Channel (DPDCH), thus sharing radio resources, such as powerresources, with the uplink physical data channels. The sharing of theradio resources results in inflexibility in radio resource allocation tothe physical HSUPA channels and the physical data channels.

The signals from different users within the same cell may interfere withone another. This type of interference is known as the intra-cellinterference. In addition, the base station also receives theinterference from the users transmitting in neighboring cells. This isknown as the inter-cell interference

When an orthogonal multiple access scheme such as Single-CarrierFrequency Division Multiple Access (SC-FDMA)—which includes interleavedand localized Frequency Division Multiple Access (FDMA) or OrthogonalFrequency Division Multiple Access (OFDMA)—is used; intra-cellmulti-user interference is not present. This is the case for the nextgeneration of the 3^(rd) generation partnership project (3GPP)enhanced-UTRA (E-UTRA) system—which employs SC-FDMA—as well as IEEE802.16e also known as Worldwide Interoperability for Microwave Access(WiMAX)—which employs OFDMA, In this case, the fluctuation in the totalinterference only comes from inter-cell interference and thermal noisewhich tends to be slower. While fast power control can be utilized, itcan be argued that its advantage is minimal.

In the uplink (UL) of OFDMA frequency division multiple access (bothclassic OFDMA and SC-FDMA) communication systems, it is beneficial toprovide orthogonal reference signals (RS), also known as pilot signals,to enable accurate channel estimation and channel quality indicator(CQI) estimation enabling UL channel dependent scheduling, and to enablepossible additional features which require channel sounding.

Channel dependent scheduling is widely known to improve throughput andspectral efficiency in a network by having the NodeB, also referred toas base station, assign an appropriate modulation and coding scheme forcommunications from and to a user equipment (UE), also referred to asmobile, depending on channel conditions such as the receivedsignal-to-interference and noise ratio (SINR). In addition to channeldependent time domain scheduling, channel dependent frequency domainscheduling has been shown to provide substantial gains over purelydistributed or randomly localized (frequency hopped) scheduling inOFDMA-based systems. To enable channel dependent scheduling, acorresponding CQI measurement should be provided over the bandwidth ofinterest. This CQI measurement may also be used for link adaptation,interference co-ordination, handover, etc.

Several control signaling information bits on downlink transmission needto be transmitted in uplink, as described in 3GPP TR 25.814 v7.0.0. 3rdGeneration Partnership Project; Technical Specification Group RadioAccess Network; Physical layer aspects for evolved Universal TerrestrialRadio Access (UTRA). For example, downlink hybrid Automatic RepeatreQuest (ARQ) (HARQ) requires a 1-bit ACK/NACK in uplink for eachreceived downlink transport block. Further, the downlink channel qualityindicator (CQI) needs to be feedback in the uplink to support frequencyselective scheduling in the downlink. When a UE (user equipment) hasuplink data transmission, the downlink ACK/NACK and/or CQI can betransmitted along with the uplink data, in which the uplink referencesignal can be used for coherent demodulation of the uplink data, as wellas the downlink ACK/NACK and/or CQI. In case there is no uplink datatransmission, a reference signal can be transmitted for coherentdemodulation of the downlink ACK/NACK and/or CQI. Thus, multiplededicated time-frequency resource blocks are necessary for the referencesignal and the ACK/NACK and/or CQI. While CQI may be transmitted lessfrequently based on a periodic or triggered mechanism, ACK/NACK needs tobe transmitted in a timely manner for every received downlink transportblock to support HARQ. Note that ACK/NACK is sometimes denoted as ACKNAKor just simply ACK, or any other equivalent term.

User equipments (UE) of an E-UTRAN network are time and frequencymultiplexed on a shared channel (SCH) such that time (approximately 1μs) and frequency synchronization are required. The scheduler, in thebase-station, has full control of the time and frequency locations ofuplink transmissions for all connected user devices, except for UEautonomous transmissions through either the (non-synchronized) randomaccess channel (RACH) channel or the scheduling request (SR) channel. Toenable proper scheduling and multi-UE management, each UE should beuniquely identified to a base-station. The 3GPP working groups haveproposed a 16-bit identifier (ID) for UE's, which represents significantoverhead costs for uplink and downlink control signaling in an E-UTRANnetwork because, in practical implementations, at most a few hundredUE's (compared to 2¹⁶) will be maintained in uplink synchronization. Anuplink synchronized UE can request and have access to uplinktransmissions faster than a non-synchronized UE, which first needs torecover synchronization.

In E-UTRA, the non-synchronized physical random access channel (PRACH)is a contention-based channel multiplexed with scheduled data in aTDM/FDM manner. It is accessible during PRACH slots of duration T_(RA)and period T_(RA).

SUMMARY OF THE INVENTION

An embodiment of the present invention provides a method fortransmitting in a cellular network. User equipment (UE)-initiatedaccesses within a cellular network are optimized to account for cellsize and to reduce signaling overhead. A fixed set of preamble parameterconfigurations for use across a complete range of cell sizes within thecellular network is established and stored within each UE. A UE locatedin a given cell receives a configuration number transmitted from a nodeBserving the cell, the configuration number being indicative of a size ofthe cell. The UE selects a preamble parameter configuration from thefixed set of preamble parameter configurations in response to thereceived configuration number and then transmits a preamble from the UEto the nodeB using the preamble parameter configuration indicated by theconfiguration number.

BRIEF DESCRIPTION OF THE DRAWINGS

Particular embodiments in accordance with the invention will now bedescribed, by way of example only, and with reference to theaccompanying drawings:

FIG. 1 is a pictorial of an illustrative telecommunications network thatsupports transmission of multiplexed RA preambles;

FIG. 2 is an illustrative up-link time/frequency allocation for use inthe network of FIG. 1;

FIG. 3 illustrates a non-synchronized physical random access channel(PRACH) preamble structure in time domain for use in the uplinktransmission of FIG. 2;

FIG. 4 is an illustration of the PRACH preamble structure in frequencydomain for use in the uplink transmission of FIG. 2;

FIG. 5 is a flow diagram illustrating operation of a signaling processfor selecting a preamble configuration for transmission of the preambleof FIG. 3;

FIG. 6 is a block diagram of an illustrative transmitter fortransmitting the preamble structure of FIG. 3;

FIG. 7A is a block diagram of an illustrative receiver for receiving thepreamble structure of FIG. 3;

FIG. 7B is a plot of a power delay profile of an example root sequencereceived by the receiver of FIG. 7A;

FIG. 8 is a block diagram illustrating the network system of FIG. 1; and

FIG. 9 is a block diagram of a cellular phone for use in the network ofFIG. 1.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Disclosed herein are various systems and methods for employing a randomaccess channel in a wireless network to accommodate user equipmentoperating in cells of varying sizes. Embodiments of the disclosedinvention may be used to access a wireless network, such as atelecommunications system, employing random access techniques. A varietyof wireless networks employ random access techniques, for example theEnhanced Universal Terrestrial Radio Access Network (E-UTRAN), currentlybeing standardized by the 3GPP working groups. The disclosed embodimentsof the invention are applicable to all such networks. The disclosedembodiments include apparatus for transmitting random access signals anda method for transmitting a random access signal optimized for cellularcoverage.

Embodiments of the present disclosure are directed, in general, towireless communication systems, and can be applied to generate randomaccess transmissions. Random access transmissions may also be referredto as ranging transmissions, or other analogous terms.

User Equipment (“UE”) may be either up-link (“UL”) synchronized or ULnon-synchronized. That is, UE transmit timing may or may not be adjustedto align UE transmissions with NodeB transmission time slots. When theUE UL has not been time synchronized, or has lost time synchronization,the UE can perform a non-synchronized random access to requestallocation of up-link resources. Additionally, a UE can performnon-synchronized random access to register itself at the access point,or for numerous other reasons. Possible uses of random accesstransmission are many, and do not restrict the scope of the presentdisclosure. For example, the non-synchronized random access allows theNodeB to estimate, and if necessary, to adjust the UE's transmissiontiming, as well as to allocate resources for the UE's subsequent up-linktransmission. Resource requests from UL non-synchronized UEs may occurfor a variety of reasons, for example: new network access, data ready totransmit, or handover procedures.

FIG. 1 shows an illustrative wireless telecommunications network 100.The illustrative telecommunications network includes base stations 101,102, and 103, though in operation, a telecommunications network mayinclude more base stations or fewer base stations. Each of base stations101, 102, and 103 is operable over corresponding coverage areas 104,105, and 106. Each base station's coverage area is further divided intocells. In the illustrated network, each base station's coverage area isdivided into three cells. Handset or other UE 109 is shown in Cell A108, which is within coverage area 104 of base station 101. Base station101 is transmitting to and receiving transmissions from UE 109. As UE109 moves out of Cell A 108, and into Cell B 107, UE 109 may be “handedover” to base station 102. Assuming that UE 109 is synchronized withbase station 101, UE 109 likely employs non-synchronized random accessto initiate handover to base station 102. The distance over which arandom access signal is recognizable by base station 101 is a factor indetermining cell size.

When UE 109 is not up-link synchronized with base station 101,non-synchronized UE 109 employs non-synchronous random access (NSRA) torequest allocation of up-link 111 time or frequency or code resources.If UE 109 has data ready for transmission, for example, traffic data,measurements report, tracking area update, etc., UE 109 can transmit arandom access signal on up-link 111 to base station 101. The randomaccess signal notifies base station 101 that UE 109 requires up-linkresources to transmit the UE's data. Base station 101 responds bytransmitting to UE 109, via down-link 110, a message containing theparameters of the resources allocated for UE 109 up-link transmissionalong with a possible timing error correction. After receiving theresource allocation and a possible timing adjustment message transmittedon down-link 110 by base station 101, UE 109 may adjust its transmittiming, to bring the UE 109 into synchronization with base station 101,and transmit the data on up-link 111 employing the allotted resourcesduring the prescribed time interval.

FIG. 2 illustrates an exemplary up-link transmission frame 202, and theallocation of the frame to scheduled and random access channels. Theillustrative up-link transmission frame 202, comprises a plurality oftransmission sub-frames. Sub-frames 203 are reserved for scheduled UEup-link transmissions. Interspersed among scheduled sub-frames 203, aretime and frequency resources allocated to random access channels 201,210. In the illustration of FIG. 2, a single sub-frame supports tworandom access channels. Note that the illustrated number and spacing ofrandom access channels is purely a matter of convenience; a particulartransmission frame implementation may allocate more or less resource torandom access channels. Including multiple random access channels allowsmore UEs to simultaneously transmit a random access signal withoutcollision. However, because each UE independently chooses the randomaccess channel on which it transmits, collisions between UE randomaccess signals may occur.

FIG. 3 illustrates an embodiment of a random access signal 300. Theillustrated embodiment comprises cyclic prefix 302, random accesspreamble 304, and guard interval 306. Random access signal 300 is onetransmission time interval 308 in duration. Transmission time interval308 may comprise one or more sub-frame 203 durations. Note that the timeallowed for random access signal transmission may vary, and thisvariable transmission time may be referred to as transmitting over avarying number of transmission time intervals, or as transmitting duringa transmission time interval that varies in duration. This disclosureapplies the term “transmission time interval” to refer to the timeallocated for random access signal transmission of any selectedduration, and it is understood that this use of the term is equivalentto uses referring to transmission over multiple transmission timeintervals. The time period allotted for random access signaltransmission may also be referred to as a random access time slot.

Cyclic prefix 302 and guard interval 306 are typically of unequalduration. Guard interval 306 has duration equal to approximately themaximum round trip delay of the cell while cyclic prefix 302 hasduration equal to approximately the sum of the maximum round trip delayof the cell and the maximum delay spread. As indicated, cyclic prefixand guard interval durations may vary from the ideal values of maximumround trip delay and maximum delay spread while effectively optimizingthe random access signal to maximize coverage. All such equivalents areintended to be within the scope of the present disclosure.

Round trip delay is a function of cell size, where cell size is definedas the maximum distance d at which a UE can interact with the cell'sbase station. Round trip delay can be approximated using the formulat=d*20/3 where t and d are expressed in microseconds and kilometersrespectively. The round-trip delay is the two-way radio propagationdelay in free space, which can be approximated by the delay of theearlier radio path. A typical earlier path is the line-of-sight path,defined as the direct (straight-line) radio path between the UE and thebase station. When the UE is surrounded by reflectors, its radiatedemission is reflected by these obstacles, creating multiple, longertraveling radio paths. Consequently, multiple time-delayed copies of theUE transmission arrive at the base station. The time period over whichthese copies are delayed is referred to as “delay spread,” and forexample, in some cases, 5 μs may be considered a conservative valuethereof.

Cyclic prefix 302 serves to absorb multi-path signal energy resultingfrom reflections of a signal transmitted in the prior sub-frame, and tosimplify and optimize equalization at the NodeB 101 receiver by reducingthe effect of the channel transfer function from a linear (or aperiodic)correlation to a cyclic (or periodic) correlation operated across theobservation interval 310. Guard interval 306 follows random accesspreamble 304 to prevent interference between random access preamblesignal 304 and any transmission in the subsequent sub-frame on the sametransmission frequencies used by random access preamble signal 304.

Random access preamble signal 304 is designed to maximize theprobability of preamble detection by the NodeB and to minimize theprobability of false preamble detections by the NodeB, while maximizingthe total number of resource opportunities. Embodiments of the presentdisclosure utilize constant amplitude zero autocorrelation (“CAZAC”)sequences to generate the random access preamble signal. CAZAC sequencesare complex-valued sequences with the following two properties: 1)constant amplitude (CA), and 2) zero cyclic autocorrelation (ZAC).

The preamble sequence is a long CAZAC complex sequence allocated to theUE among a set of R_(S) possible sequences. These sequences are builtfrom cyclic shifts of a CAZAC root sequence. If additional sequences areneeded, they are built from cyclic shifts of other CAZAC root sequences.

Well known examples of CAZAC sequences include, but are not limited to:Chu Sequences, Frank-Zadoff Sequences, Zadoff-Chu (ZC) Sequences, andGeneralized Chirp-Like (GCL) Sequences. A known set of sequences withCAZAC property is the Zadoff-Chu N-length sequences defined as follows

$a_{k} = {\exp \left\lbrack {{- j}\; 2\pi \frac{M}{N}\left( {\frac{k\left( {k + 1} \right)}{2} + {qk}} \right)} \right\rbrack}$

where M is relatively prime to N, N odd, and q any integer.

The latter constraint on N also guarantees the lowest andconstant-magnitude cross-correlation √{square root over (N)} betweenN-length sequences with different values of M: M₁, M₂ such that (M₁-M₂)is relatively prime to N. As a result, choosing N a prime number alwaysguarantees this property for all values of M<N, and therefore maximizesthe set of additional sequences, non orthogonal, but with optimalcross-correlation property. On top of providing additional sequences fora UE to chose among in a given cell, these sequences are also intendedto be used in neighboring cells, so as to provide good inter-cellinterference mitigation. In this disclosure, the terms: Zadoff-Chu, ZC,and ZC CAZAC, are used interchangeably. The term CAZAC denotes any CAZACsequence, ZC or otherwise.

In various embodiments of the present disclosure, random access preamblesignal 304 comprises a CAZAC sequence, such as a ZC sequence. Additionalmodifications to the selected CAZAC sequence can be performed using anyof the following operations: multiplication by a complex constant, DFT,IDFT, FFT, IFFT, cyclic shifting, zero-padding, sequenceblock-repetition, sequence truncation, sequence cyclic-extension, andothers. Thus, in one embodiment of the present disclosure, a UEconstructs random access preamble signal 304 by selecting a CAZACsequence, possibly applying a combination of the described modificationsto the selected CAZAC sequence, modulating the modified sequence, andtransmitting the resulting random access signal over the air.

Assuming that a preamble duration allowing reliable detection at thecell perimeter has been selected, random access channel coverage ismaximized by allocating as much of the transmission time interval aspossible to round trip delay. In a typical embodiment of the invention,the maximum round trip delay is taken to be one half of what is left ofthe transmission time interval 308 after subtracting the preambleduration 304 and the maximum delay spread.

Maximum Round Trip Delay=(TTI−Preamble Duration−Delay Spread)/2

Guard interval 306 is approximately a maximum round trip delay induration to allow for mis-timing of the random access transmissionwhile, in the worst-case of a cell-edge UE, the tail (or delay spread)of the preamble is absorbed by the cyclic prefix of the subsequent TTI.The cyclic prefix 302 is set to a duration of approximately the sum ofthe maximum round trip delay and the maximum delay spread. Thisdimensioning of the cyclic prefix 302 and the guard interval 306 servesto maximize the cell radius over which the random access channel iseffective while maintaining isolation from adjacent TTIs.

An alternative embodiment of a random access signal may assign aduration of maximum round trip delay plus maximum spread delay to boththe cyclic prefix and the guard interval. This dimensioning needlesslyallocates a delay spread duration to the guard interval that couldotherwise be used to increase round trip delay and thereby increase cellradius.

Further aspects of embodiments of the Random Access (RA) channeloperation are described in related U.S. patent application Ser. No.11/691,549 filed 27 Mar. 2007, now U.S. Pat. No. 8,098,745, entitled“Random Access Structure For Wireless Networks” which is incorporatedherein by reference; and in related U.S. patent application Ser. No.11/833,329, filed 3 Aug. 2007, now U.S. Pat. No. 8,259,598, entitled“Random Access Structure For Optimal Cell Coverage” which isincorporated by reference herein.

Referring again to FIG. 1, UE 109 is traveling in a direction with aground speed as indicated by 112. The direction and ground speed resultsin a speed component that is relative to serving NodeB 101. Due to thisrelative speed of UE moving toward or away from its serving NodeB aDoppler shift occurs in the signals being transmitted from the UE to theNodeB resulting in a frequency shift and/or frequency spread that isspeed dependent.

The excellent auto/cross-correlation of CAZAC sequences allowssupporting a much larger number of signature opportunities, 64, than the16 Walsh-Hadamard opportunities offered in the one version of a UMTSrandom access channel (RACH) preamble, and this with very littleperformance loss, even when two or more preambles are received in thesame Random Access slot. However, the above performance assumes no orlittle Doppler spread or frequency shift, in presence of which, theCS-ZC sequence looses its zero-auto-correlation property. The latterdegradation has been confirmed by simulations; in one such simulationthe result is as follows: the wrong preamble detection rate when one ormore preambles were sent rises up to 1% and 50% at 120 km/h and 360 km/hrespectively, in the E_(P)/N₀ region of 18 dB, which is the RACH targetSINR for detection and false alarm (in presence of noise only)probabilities of 0.99 and 10⁻² respectively.

The current E-UTRA requirements regarding the performance of high-speedUE's is specified in as follows: The E-UTRAN shall support mobilityacross the cellular network and should be optimized for low mobile speedfrom 0 to 15 km/h. Higher mobile speed between 15 and 120 km/h should besupported with high performance. Mobility across the cellular networkshall be maintained at speeds from 120 km/h to 350 km/h (or even up to500 km/h depending on the frequency band) . . . . The mobile speed above250 km/h represents special case, such as high-speed train environment.In such case a special scenario applies for issues such as mobilitysolutions and channel models. For the physical layer parameterizationE-UTRAN should be able to maintain the connection up to 350 km/h, oreven up to 500 km/h depending on the frequency band. Such requirementscan be summarized as: the physical layer should be dimensioned so as tooptimize the performance of low-speed UE's while keeping acceptableperformance for high-speed UE's.

In order to fulfill the E-UTRAN requirements, the PRACH preamblesequence length design should address the following requirements: 1)maximize the number of Zadoff-Chu sequences with optimalcross-correlation properties; 2) minimize the interference to/from thesurrounding scheduled data on the Physical Uplink Scheduled Channel(PUSCH).

The former is guaranteed by choosing a prime-length sequence. For thelatter, since data and preamble OFDM symbols are neither aligned norhave same durations, strict orthogonality cannot be achieved. At least,fixing the preamble duration to an integer multiple of the PUSCH symbolprovides some commensurability between preamble and PUSCH sub-carriersthus providing orthogonality between some sub-carriers. This alsoassumes that the preamble sampling frequency is an integer multiple ofthe data symbol sub-carrier spacing. This is achieved with the chosenallocated bandwidth of seventy-two data symbol sub-carriers for thePRACH preamble. However, with 800 μs duration, the resulting sequencelength is 864, which does not provide the prime number of requirementone above. Therefore shortening the preamble to a prime length slightlyincreases the interference between PUSCH and NSRA by slightly decreasingthe preamble sampling rate

FIG. 4 is a more detailed illustration of the PRACH preamble structurefor use in the uplink transmission of FIG. 2. Preamble structure 402represents the output of the data symbol FFT of the transmitterillustrating the seventy-two sub-carriers 404 that are each 15 kHz,while preamble structure 406 represents the output of the preamble DFTof the transmitter illustrating the 864 sub-carriers 408 that are each1.25 kHz. This embodiment uses guard bands 412, 414 to avoid the datainterference at preamble edges. A cautious design of preamble sequencelength not only retains a high inherent processing gain, but also allowsa decent avoidance of strong data interference. In addition, the loss ofspectral efficiency by guard sub-carriers reservation can also be wellcontrolled at a fine granularity. In this embodiment, each sub-carrier408 is 1.25 kHz for 800 μs preamble duration.

The sequence length 410 of 839 preamble symbol sub-carriers also is abest trade-off choice since it corresponds to 69.91 symbol sub-carriersin each symbol and offers 72−69.91=2.09 symbol sub-carriers protection,which is very close to 1 symbol sub-carrier protection one each side ofthe preamble. Further higher/lower prime sequence length adjustments donot provide as good of integer number sub-carrier protection. Moreexactly, the 839 preamble sub-carriers 410 are mapped onto the 864allocated sub-carriers 408 as follows: twelve and a half zerosub-carriers 412; 839 preamble sub-carriers 410; twelve and a half zerosub-carriers 414. In another embodiment, guard band 412 may be thirteensub-carries while guard band 414 is twelve sub-carriers, or visa-versa.In yet another embodiment, the guard bands may comprise other numericalcombinations of sub-carriers.

The time-continuous PRACH preamble signal s(t) is defined by:

${s(t)} = {\beta_{PRACH}{\sum\limits_{k = 0}^{N_{ZC} - 1}\; {\sum\limits_{n = 0}^{N_{ZC} - 1}\; {{x_{u,v}(n)} \cdot e^{{- j}\frac{2\pi \; {nk}}{N_{ZC}}} \cdot e^{j\; 2{\pi {({k + \phi + {K{({k_{0} + {1\text{/}2}})}}})}}\Delta \; {f_{RA}{({t - T_{CP}})}}}}}}}$

where

0≤t<T _(SEQ) +T _(CP),

β_(PRACH) is an amplitude scaling factor and

k ₀ =k _(RA) N _(sc) ^(RB) −N _(RB) ^(UL) N _(sc) ^(RB)/2.

T_(SEQ) is the sequence duration and T_(CP) is the cyclic prefixduration. N_(sc) ^(RB) is the number of data subcarriers per resourceblock (RB) and N_(RB) ^(UL) is the total number of resource blocksavailable for UL transmission. The location in the frequency domain iscontrolled by the parameter k_(RA), expressed as a resource block numberconfigured by higher layers and fulfilling

0≤k _(RA) ≤N _(RB) ^(UL)−6.

The factor

K=Δf/Δf _(RA)

accounts for the difference in subcarrier spacing between the randomaccess preamble and uplink data transmission. The variable φ defines afixed offset determining the frequency-domain location of the randomaccess preamble within the resource blocks. The PRACH signal takes thefollowing value for φ: φ=7.

Number of Root Sequences and Cyclic Shift Values

If a base station can select any number of cyclic shifts from 0 to 838,then ten or more signaling bits would be required on the broadcastchannel (BCH). It has now been determined that a fixed set of preambleparameter configurations can be established for use across a completerange of cell sizes. An approach for signaling a cyclic shift valueN_(CS) to be used in a cell is to reduce the full range of possiblecyclic shifts to a pre-defined set of cyclic shift configurations.Sixteen different configurations allow reducing the cyclic shiftsignaling to four bits. The criterion for choosing these cyclic shiftvalues is to minimize the number of Zadoff-Chu root sequences whilemaximizing the associated cell range. In other words, a configurationusing r different root sequences should be fully filled with cyclicshifted preambles before another root sequence is added. Given thatsixty-four signatures must be generated, a first choice is all cyclicshift values corresponding to splitting the sequence length intosub-multiples of 64: N_(CS)=N/k; k=1, 2, 4, 8, 16, 32, 64. Table 1 showsthe seven resulting N_(CS) values where all root sequences generate thesame number of cyclic shifted preambles. The number of root sequences isgiven for the regular case where no cyclic shift restrictions apply (lowto medium speed cell).

In the following tables, the cell size is illustrative and each networkoperator can have its own way of calculating it, given a number of guardsamples, typical delay spread, etc. The cell size column gives anexample of cell sizes derivations assuming two guard samples and 5 μsdelay spread.

TABLE 1 Cyclic shift values maximizing the cell size while minimizingthe number of root sequences # of root # of cyclic sequences shifts perroot (no cyclic shift Cyclic shift seq. restrictions) (samples) Cellsize (km) 64 1 13 0.82 32 2 26 2.68 16 4 52 6.40 8 8 104 13.83 4 16 20928.85 2 32 419 58.89 1 64 0 118.96

However, the above list is somewhat restrictive in that it does notprovide any intermediate configuration between two and four rootsequences, or between four and eight root sequences. Therefore, theabove rule for maximizing the cell size for a given number of rootsequences is extended to all possible numbers of root sequences. For agiven number of root sequences, the cyclic shift value is chosen toprovide a close to equal number of cyclic shifts per root sequence, thusmaximizing the corresponding cell size. The next number of rootsequences is the minimum number of root sequences required to carry 64signatures when the cyclic shift of the previous configuration isincremented by one sample. This results in some skipped numbers of rootsequences. This algorithm actually provides fifteen different numbers ofroot sequences. In order to make best use of the four bits available tocarry this information, another configuration is added. In thisembodiment, an intermediate configuration in between one and two rootsequences is added. This is to provide a finer granularity at small cellsizes. Also, it provides an additional configuration for the two-rootsequence case, with an unbalanced number of cyclic shifted preambleopportunities between the two root sequences, thus reducing the rootsequence collision probability. If such an unbalanced allocation ofcyclic shifted preambles to root sequences is to be used, it is the mostuseful for the two-root sequence case. Thus, the fixed set of preambleparameter configurations sample the continuous cell size range coveredby the network in a non-linear way, such that a finer configurationgranularity is provided for smaller cells, reflecting the broaderdeployment of smaller cells compared to larger cells. Table 2 providesthe final cyclic shift set.

TABLE 2 PRACH preamble parameters for pre-defined cell configurations #of root # of cyclic sequences root shifts per root (no cyclic shiftCyclic shift Configuration # sequences seq. restrictions) (samples) Cellsize (km) 1 All 64 1 13 0.82 2 1 20 2 19 1.68 2 44 3 All 32 2 26 2.68 4All but last 21 3 38 4.39 Last 22 5 All 16 4 52 6.40 6 All but last 13 564 8.11 Last 12 7 All but last 11 6 76 9.83 Last 9 8 All but last 9 7 8310.83 Last 10 9 All 8 8 104 13.83 10 1-2  4 10 119 15.98 3-10 7 11 Allbut last 6 11 139 18.84 Last 4 12 All but last 5 13 167 22.84 Last 4 13All 4 16 209 28.85 14 All but last 3 22 279 38.86 Last 1 15 All 2 32 41958.89 16 All 1 64 0 118.96

Table 3 shows, for the regular case where no cyclic shift restrictionsapply (low to medium speed cell) an alternative embodiment of a selectedset of number of root sequences, chosen to provide a close to equalnumber of cyclic shifts per root sequence. When this is not possible,the rule applied is to have an equal number of cyclic shifts for allroot sequences but the last one, and to adjust the remaining number ofcyclic shifts in the last root sequence to yield 64 in total. Theassociated cell size is provided, for information, and is derived fromcyclic shift value assuming two guard samples and 5 μs maximum delayspread. The goal is to always try to minimize the number of rootsequences for a given cell range. Since there are eleven differentconfigurations, the configuration can be signaled on 4 bits.

TABLE 3 PRACH preamble parameters for pre-defined cell configurations #of ZC # of cyclic sequences ZC shifts per ZC (no cyclic shift Cyclicshift Configuration # sequences seq. restrictions) (samples) Cell size(km) 1 All 64 1 13 0.8 2 All 32 2 26 2.7 3 All but last 21 3 38 4.4 Last22 4 All 16 4 52 6.4 5 All but last 13 5 64 8.1 Last 12 6 All but last11 6 76 9.8 Last 9 7 All 8 8 104 13.8 8 All but last 6 11 139 18.8 Last4 9 All but last 5 13 167 22.8 Last 4 10 All 4 16 209 28.8 11 All 1 64839 119.0

For high speed cells where cyclic shift restrictions apply, more ZC rootsequences will be configured than what is indicated in the Table 2 andTable 3. The NodeB signals both the cell configuration number, whichidentifies the cyclic shift value, and the additional number of ZC rootsequences. Whenever the number of additional ZC root sequences isgreater than zero, the UE infers that cyclic restrictions apply andidentifies which cyclic shifts must not be used according to operatingprocedures of the telecommunications network in which the UE isoperating.

In an alternate embodiment, the NodeB only signals with a one-bit flagif the current cell is a high speed cell or a normal cell. In the formercase, the UE infers that cyclic restrictions apply and identifies whichcyclic shifts must not be used and associated additional root sequencesaccording to operating procedures of the telecommunications network inwhich the UE is operating.

Table 2 and Table 3 provide two representative examples of a fixed setof preamble parameters. Other embodiments may use variations of theseexamples by agreeing upon a different fixed set of preamble parametersthat is stored in each UE used in the network. In another embodiment,the number of configurations may be increased to up to thirty-two andtherefore five bits be used for signaling, for example.

FIG. 5 is a flow diagram illustrating operation of a signaling processfor selecting a preamble configuration for transmission of the PRACHpreamble of FIG. 3 from user equipment to base stations. The fixed setof preamble parameter configurations for use across a complete range ofcell sizes within the cellular network is established 502 as discussedabove. Once established, each UE that will operate in the network ispreloaded with the fixed set of preamble configurations. In the presentembodiment, this is done by loading the fixed set of preambleconfigurations into a storage circuit, such as a flash read only memory(EPROM) or other type of random access memory device, in an offlineprocedure. In another embodiment, the storage circuit may by loaded orupdated via data downloads from a eNB or other control system within thenetwork using over the air transmissions. The fixed set of preambleparameter configurations may be stored on the UE in the form of a recordor table that can be accessed using the configuration number as anindex, for example.

In addition to the fixed set of parameter configurations that ispreloaded onto all UEs in the cellular network, the ordering of rootsequences and the rule for physical mapping of the signatures onto theroot sequences is preloaded onto all UEs that will operate within thenetwork.

As a UE enters a cell, an eNB serving that cell broadcasts controlsignaling information to the UE to notify the UE as to what preambleconfiguration to use within that cell. The eNB also broadcasts the indexof the first root sequence of the set of preloaded root sequences andinformation of whether high speed cyclic shift restrictions apply withinthe cell. The UE receives 504 a configuration number from the eNB thatis correlated to the size of the cell, as described in Table 2 for thisembodiment. For example, if the cell size is between 4.26 km and 6.2 km,then the eNB sends a four-bit configuration number of “0x5” whichimplicitly indicates to the UE to form a preamble based on configurationparameters of sixteen cyclic shifts per root sequence using four rootsequences, as illustrated in Table 2.

After receiving the configuration number, the UE will store this valuefor future reference. When it is time to transmit a PRACH preamble, theUE selects a preamble parameter configuration specified by the receivedconfiguration number from the fixed set of preamble parameterconfigurations. Following the same example, the UE will select parameterconfiguration “5” meaning that it will use the implicit values of fourroot sequences and sixteen cyclic shifts per root sequence or in otherwords each cyclic shift will shift fifty-two sample positions.

The UE will then transmit 508 an NSRA preamble to the eNB using thepreamble parameter configuration indicated by the configuration number.

Before transmitting the preamble, the UE determines 510 the cyclic shiftvalue and/or the number of root sequences of the selected preambleparameter configuration by consulting the stored fixed set of preambleparameter configurations using the received configuration number as anindex in this embodiment. Other embodiments may use other schemes toassociate the received configuration number with a correspondingpreamble configuration of the fixed set of preamble parameterconfigurations that is stored on the UE.

In this embodiment there are sixty-four preamble signatures that may beused by any UE within a given cell. The UE maps 512 the sixty-fourpreamble signatures to subsequent cyclic shifts of a given root sequenceaccording to the number of cyclic shifts until the given root sequenceis full. Generally one root sequence will not accommodate all sixty-foursignatures and mapping continues to additional root sequences for all ofthe number of root sequences until a last root sequence. If the lastsequence has a different number of cyclic shifts as indicated by theselected parameter configuration, then the UE may adjust 512 the numberof cyclic shifts mapped onto the last root sequence such that thepredetermined number (64) of preamble signatures are mapped.

After mapping the preamble signatures, the UE selects 514 one of themapped preamble signatures for use in transmitting 508 the preamble.There are sixty-four total possible signatures. This set is split asfollows: 1) contention-based signatures; and 2) contention-freesignatures. The contention-based signature set is split into twosub-sets small and large resource allocation of msg3.

Contention-free signatures are explicitly allocated to a UE by the eNBin the case of handover and new downlink data in buffer for anon-synchronized UE.

Contention-based signatures are selected by the UE as follows. First,the UE chooses the relevant subset based on the size of the UL resourceit needs to send as a variable size message (msg3) on the physicaluplink shared channel (PUSCH) after the preamble. The UE estimates thesize of the UL resource based on msg3 payload and quality of the radiolink; the poorer the radio link quality, the smaller the allocatedbandwidth. Then, the UE picks a signature randomly within the selectedsignature subset.

Regardless of whether the request is contention-based orcontention-free, in this embodiment the transmission will use the samephysical random access channel (PRACH) and preamble structure, asdescribed herein. Of course, in other embodiments the contention-freetransmissions may be transmitted using a variation of this scheme or adifferent scheme.

FIG. 6 is a block diagram of an illustrative transmitter 600 fortransmitting the preamble structure of FIG. 3. Apparatus 600 comprisesZC Root Sequence Selector 601, Cyclic Shift Selector 602, RepeatSelector 603, ZC Root Sequence Generator 604, Cyclic Shifter 605, DFT in606, Tone Map 607, other signals or zero-padding in 611, IDFT in 608,Repeater in 609, optional repeated samples 612, Add CP in 610, and thePRACH signal in 613. Elements of the apparatus may be implemented ascomponents in a fixed or programmable processor. In some embodiments,the IDFT block in 608 may be implemented using an Inverse Fast FourierTransform (IFFT), and the DFT block in 606 may be implemented using aFast Fourier Transform (FFT). Apparatus 600 is used to select andperform the PRACH preamble signal transmission as follows. The UEperforms selection of the CAZAC (e.g. ZC) root sequence using the ZCRoot Sequence Selector 601 and the selection of the cyclic shift valueusing the Cyclic Shift Selector 602. Next, the UE generates the ZCsequence using the ZC Root Sequence Selector 604. Then, if necessary,the UE performs cyclic shifting of the selected ZC sequence using theCyclic Shifter 605. The UE performs DFT (Discrete Fourier Transform) ofthe cyclically shifted ZC sequence in DFT 606. The result of the DFToperation is mapped onto a designated set of tones (sub-carriers) usingthe Tone Map 607. Additional signals or zero-padding 611, may or may notbe present. The UE next performs IDFT of the mapped signal using theIDFT 608. The size of the IDFT in 608 may optionally be larger than thesize of DFT in 606.

In other embodiments, the order of cyclic shifter 605, DFT 606, tone map607 and IDFT 608 may be arranged in various combinations. For example,in one embodiment a DFT operation is performed on a selected rootsequence, tone mapping is then performed, an IDFT is performed on themapped tones and then the cyclic shift may be performed. In anotherembodiment, tone mapping is performed on the root sequence and then anIDFT is performed on the mapped tones and then a cyclic shift isperformed.

FIG. 7A is a block diagram of an illustrative receiver for receiving thepreamble structure of FIG. 3. This receiver advantageously makes use ofthe time and frequency domain transforming components used to map andde-map data blocks in the up-link sub-frame to take full profit of thePRACH format and CAZAC sequence by computing the PRACH power delayprofile through a frequency-domain computed periodic correlation.Indeed, the power delay profile pdp(l) of the received sequence isdefined as:

$\begin{matrix}{{{pdp}_{yx}(l)} = {{{r_{yx}(l)}} = {{\sum\limits_{n = 0}^{N_{ZC} - 1}\; {{y(n)}{x^{*}\left( \left( {n + l} \right)_{N_{ZC}} \right)}}}}}} & (1)\end{matrix}$

where r_(yx)(l) is the discrete periodic autocorrelation function at lagl of the received sequence y(n) and the reference searched CAZACsequence x(n), and where ( )* and ( )_(n) denote the complex conjugateand modulo-n respectively. Given the periodic convolution of the complexsequences y(n) and x(n) defined as:

$\begin{matrix}{{\left\lbrack {{y(n)}*{x(n)}} \right\rbrack (l)} = {\sum\limits_{n = 0}^{N_{ZC} - 1}\; {{y(n)}{x\left( \left( {l - n} \right)_{N_{ZC}} \right)}}}} & (2)\end{matrix}$

r_(yx)(l) can be expressed as follows:

r _(yx)(l)=(y(n)*x*(−n))(l)  (3)

Using the following properties of the Discrete Fourier Transform (DFT):

Complex Sequence DFT

x(n)→X(k)

y(n)→Y(k)

x*(−n)→X*(k)

y(n)*x(n)→Y(k)X(k)  (4)

r_(yx)(l) can be computed in frequency domain as:

r _(yx) =DFT ⁻¹ {DFT(y(n))DFT(x(n))*}  (5)

An additional complexity reduction comes from the fact that differentPRACH signatures are generated from cyclic shifts of a common rootsequence. As illustrated in FIG. 7B, the frequency-domain computation ofthe power delay profile of a root sequence provides in one shot theconcatenated power delay profiles of all signatures carried on the sameroot sequence.

The received PRACH signal 701, comprising cyclic prefix and PRACHpreamble signal, is input to cyclic prefix removal component 702 whichstrips the cyclic prefix from the PRACH signal producing signal 703.Frequency domain transforming component DFT 704 couples to cyclic prefixremoval component 702. Frequency domain transforming component 704converts signal 703 into sub-carrier mapped frequency tones 705.Sub-carrier de-mapping component 706 is coupled to frequency domaintransforming component 704. Sub-carrier de-mapping component 706 de-mapssub-carrier mapped frequency tones 705 to produce useful frequency tones707. Product component 711 is coupled to both sub-carrier de-mappingcomponent 707 and frequency domain transforming component 709. Frequencydomain transforming component (DFT) 709 converts a preamble rootsequence 710, such as a prime length Zadoff-Chu sequence, into acorresponding set of pilot frequency tones 708. Complex conjugation ofpilot frequency tones 708 is performed using 721, to produce samples720. Product component 711 computes a tone by tone complexmultiplication of received frequency tones 707 with samples 720 toproduce a set of frequency tones 712. Time domain transforming component(IDFT) 713 is coupled to product component 711. Time domain transformingcomponent 713 converts multiplied frequency tones 712 into correlatedtime signal 714. Correlated time signal 714 contains concatenated powerdelay profiles of the cyclic shift replicas of the preamble rootsequence 710. Energy detection block 715 is coupled to time domaintransforming block 713. Energy detection block 715 identifies receivedpreamble sequences by detecting the time of peak correlation betweenreceived schedule request signal 701 and preamble root sequence 710.

Note that frequency domain transforming component 709 is called for whenusing the transmitters illustrated in FIG. 6. When using an alternativeembodiment transmitter that does not perform a DFT, frequency domaintransforming component 709 may be omitted.

FIG. 8 is a block diagram illustrating the network system of FIG. 1. Asshown in FIG. 8, the wireless networking system 115 comprises a userdevice 132 in communication with a base-station 150. The user device 132may represent any of a variety of devices such as a server, a desktopcomputer, a laptop computer, a cellular phone, a Personal DigitalAssistant (PDA), a smart phone or other electronic devices. In someembodiments, the electronic device 132 communicates with thebase-station 150 based on a LTE or E-UTRAN protocol. Alternatively,another communication protocol now known or later developed is used.

As shown, the electronic device 132 comprises a processor 138 coupled toa memory 134 and a transceiver 140. The memory 134 stores applications136 for execution by the processor 138. The applications 136 couldcomprise any known or future application useful for individuals ororganizations. As an example, such applications 136 could be categorizedas operating systems, device drivers, databases, multimedia tools,presentation tools, Internet browsers, emailers, Voice Over InternetProtocol (VOIP) tools, file browsers, firewalls, instant messaging,finance tools, games, word processors or other categories. Regardless ofthe exact nature of the applications 136, at least some of theapplications 136 may direct the user device 132 to transmit uplinksignals to the base-station 150 periodically or continuously via thetransceiver 140. Over time, different uplink transmissions from the userdevice 132 may be high priority (time-critical) or low priority(non-time critical). In at least some embodiments, the user device 132identifies a Quality of Service (QoS) requirement when requesting anuplink resource from the base-station 150. In some cases, the QoSrequirement may be implicitly derived by the base-station 150 from thetype of traffic supported by the user device 132. As an example, VOIPand gaming applications often involve high priority uplink transmissionswhile High Throughput (HTP)/Hypertext Transmission Protocol (HTTP)traffic involves low priority uplink transmissions.

As shown in FIG. 8, the transceiver 140 comprises uplink logic 120,which enables the user device 132 to request an uplink resource from thebase-station 150 and upon a successful request to send uplinktransmissions to the base-station 150. In FIG. 8, the uplink logic 120comprises resource request logic 122, synchronize logic 124, andtime-out logic 126. As would be understood by one of skill in the art,the components of the uplink logic 120 may involve the physical (PHY)layer and/or the Media Access Control (MAC) layer of the transceiver140.

In at least some embodiments, the resource request logic 122 detectswhen the user device 132, in absence of any valid uplink resource grant,needs to send an uplink transmission to the base-station 150 and submitsa corresponding scheduling request. If the user device 132 is not uplinksynchronized, the scheduling request is made using the non-synchronizedphysical random access channel (PRACH) 186, which is potentiallycontentious depending on how many other user devices also need to usethe PRACH at the same time (e.g., for scheduling requests or uplinksynchronization maintenance). Alternatively, if the user device 132 isuplink synchronized, the resource request may be submitted via acontention-free scheduling request channel 192 which may be available tothe user device 132. In either case, the request is made using preamblestructure 300, depending on the relative speed of the UE to the NodeBand how a particular cell is configured, as described earlier. A commandreceived from the base station indicates what preamble configuration isto be used in a given cell, as described in more detail above.

In at least some embodiments, the scheduling request channel 192 is partof the dedicated channels 184. The dedicated channels 184 representuplink synchronized channels which are dedicated to a particular purposeand which are selectively accessible to one or more user devices.Another example of dedicated channel is the sounding reference signal(SRS). The SRS is a standalone reference signal (or pilot) whichprovides means to the base-station to perform channel qualityinformation (CQI) estimation for frequency dependent scheduling, tomaintain uplink synchronization, and to implement link adaptation andpower control for each user.

If the user device 132 previously obtained a resource allocation fromthe base station 150 and the resource allocation has not expired, uplinktransmissions can be sent via a shared channel 182 (i.e., a channelshared with other user devices based on time and division multiplexing)in the form of a MAC Packet Data Unit (PDU) transmission. In at leastsome embodiments, the resource request logic 122 also detects when theuser device 132, with at least one valid uplink resource grant, needs toupdate its current allocated uplink resource(s) (e.g., if the userdevice 132 needs more resources because it received more data in itstransmission buffer) and submits a corresponding scheduling request.Since the user device 132 already has valid uplink grants, it is uplinksynchronized, and the resource request may be either embedded in a MACPDU sent on these valid grants on the uplink shared channel 182, orsubmitted via the scheduling request channel 192.

To use the shared channel 182 or the scheduling request channel 192, theuser device 132 receives a unique identifier from the base-station 150.In some embodiments, the unique identifier is explicitly provided by thebase-station 150 (e.g., the base-station 150 broadcasts a multi-bitunique identifier to the user device 132 for use with the shared channel182). In alternative embodiments, the unique identifier is implicitlyprovided by the base-station 150 (e.g., the base-station 150 provides aone-to-one mapping between the user device 132 and a physical uplinkresource of the scheduling request channel 192).

The synchronize logic 124 enables the user device 132 to maintain aparticular synchronization for uplink transmissions via the sharedchannel 182 or other uplink synchronized channels (e.g., the SRS or thescheduling request channel 192). In some embodiments, the synchronizelogic 124 supports time and frequency adjustments based on apredetermined protocol and/or instructions from the base-station 150.Once the user device 132 is synchronized, the synchronization can beperiodically updated based on timers and/or information exchangedbetween the user device 132 and the base-station 150. For example, ifthe user device 132 is synchronized and has at least one schedulinggrant from the base-station 150, then the synchronize manager 174 of thebase-station 150 can maintain the user device's synchronization based onongoing uplink transmissions from the user device 132 via the sharedchannel 182.

If the user device 132 is synchronized but does not have a schedulinggrant from the base-station 150, then the synchronize manager 174 of thebase-station 150 can maintain the user's synchronization based on aPRACH transmission 186. Alternatively, if the user device 132 issynchronized but does not have a scheduling grant from the base-station150, then the synchronize manager 174 of the base-station 150 canmaintain the user's synchronization based on information transmitted viaone of the dedicated channels 184 (e.g., using a SRS or an autonomoussynchronization request from the user device 132 through the schedulingrequest channel 192). By appropriately synchronizing uplinktransmissions of the user device 132, interference to and from thetransmissions of other user devices can be avoided and orthogonalmultiplexing is maintained.

As shown in FIG. 8, the base-station 150 comprises a processor 154coupled to a memory 156 and a transceiver 170. The memory 156 storesapplications 158 for execution by the processor 154. The applications158 could comprise any known or future application useful for managingwireless communications. At least some of the applications 158 maydirect the base-station to manage transmissions to or from the userdevice 132.

As shown in FIG. 8, the transceiver 160 comprises an uplink resourcemanager 170, which enables the base-station 150 to selectively allocateuplink resources to the user device 132. In FIG. 8, the uplink resourcemanager 170 comprises a state manager 172, a synchronize manager 174, ascheduling grants manager 176 and a time-out manager 178. As would beunderstood by one of skill in the art, the components of the uplinkresource manager 170 may involve the physical (PHY) layer and/or theMedia Access Control (MAC) layer of the transceiver 160.

Transceiver 160 includes a receiver as described in more detail in FIG.7. As discussed previously, a management application on the NodeBdetermines what preamble configuration of a fixed set of preambleparameter configurations will be used in a particular cell, based oncell sized. The NodeB broadcasts this information to all UE in the cellas part of system and cell-specific information on a broadcast channel(BCH).

In at least some embodiments, the state manager 172 determines whetherto assign the user device 132 to a synchronized state or to anon-synchronized state. In at least some embodiments, the user device132 can request to be assigned to the synchronized state using PRACH186.

If the user device 132 is accepted into the synchronized state, areduced identifier is provided to the user device 132. The reducedidentifier enables the user device 132 to send uplink transmissions viathe shared channel 182 and new resource requests via the schedulingrequests channel 192. In some embodiments, the state manager 172 enablesthe reduced identifier to be explicitly provided to the user device 132(e.g., broadcasting a multi-bit unique identifier to the user device 132for use with the shared channel 182). In alternative embodiments, thestate manager 172 enables the unique identifier to be implicitlyprovided to the user device 132 (e.g., providing a one-to-one mappingbetween the user device 132 and a physical uplink resource of thebase-station 150). If the user device 132 becomes non-synchronized dueto a time-out or any other reason, the state manager 172 reassigns theuser device 132 to the non-synchronized state and releases the reducedidentifier and any associated uplink resource that was assigned to theuser device 132.

The synchronize manager 174 maintains user devices in synchronizationfor uplink transmissions via the shared channel 182 or any dedicatedchannel 184. In order to do so, the synchronize manager 174 estimatesthe timing error of the uplink transmissions of the user device 132 oneither the shared channel 182, a dedicated channel 184 (e.g., SRS) orthe PRACH 186. Then, the synchronize manager 174 sends back a timingadvance (TA) command to the user device 132, that will be executed bythe synchronize logic 124. By appropriately synchronizing uplinktransmissions of the user device 132, the synchronize manager 174 avoidsinterferences between uplink transmissions of the user device 132 anduplink transmissions of other user devices and orthogonal multiplexingis maintained.

The scheduling grants manager 176 selectively determines whensynchronized user devices will be scheduled on the shared channel 182.For example, the scheduling grants manager 176 may assign schedulinggrants in response to new resource requests from user device 132 sentthrough the scheduling request channel 192.

If more than a threshold amount of time passes during which the userdevice 132 does not send any uplink transmissions, a time-out may occur.The time-out manager 178 determines when a time-out occurs based on oneor more time-out thresholds 190. In at least some embodiments, thetime-out manager 178 implements timers or counters to track the amountof time that passes between uplink transmissions for all synchronizeduser devices. The time-out thresholds 190 may be predetermined or may bedetermined, for example, based on the number of user devices incommunication with the base-station.

In at least some embodiments, a time-out threshold causes user devicesto enter the non-synchronized state. Typically, the entrance of userdevices to the non-synchronized state does not depend on exchangingmessages between the base station 150 and user devices. In other words,both user devices and the base-station 150 can track the passage of timeseparately and independently determine that a user device is in anon-synchronized state. In case a user device transitions to thenon-synchronized state, any existing uplink grant of this user device isreleased.

FIG. 9 is a block diagram of a UE 1000 that stores a fixed set ofpreamble parameter configurations for use across a complete range ofcell sizes within the cellular network, as described above. Digitalsystem 1000 is a representative cell phone that is used by a mobileuser. Digital baseband (DBB) unit 1002 is a digital processing processorsystem that includes embedded memory and security features.

Analog baseband (ABB) unit 1004 performs processing on audio datareceived from stereo audio codec (coder/decoder) 1009. Audio codec 1009receives an audio stream from FM Radio tuner 1008 and sends an audiostream to stereo headset 1016 and/or stereo speakers 1018. In otherembodiments, there may be other sources of an audio stream, such acompact disc (CD) player, a solid state memory module, etc. ABB 1004receives a voice data stream from handset microphone 1013 a and sends avoice data stream to handset mono speaker 1013 b. ABB 1004 also receivesa voice data stream from microphone 1014 a and sends a voice data streamto mono headset 1014 b. Usually, ABB and DBB are separate ICs. In mostembodiments, ABB does not embed a programmable processor core, butperforms processing based on configuration of audio paths, filters,gains, etc being setup by software running on the DBB. In an alternateembodiment, ABB processing is performed on the same processor thatperforms DBB processing. In another embodiment, a separate DSP or othertype of processor performs ABB processing.

RF transceiver 1006 includes a receiver for receiving a stream of codeddata frames and commands from a cellular base station via antenna 1007and a transmitter for transmitting a stream of coded data frames to thecellular base station via antenna 1007. A command received from the basestation indicates what configuration number of the fixed set of preambleparameter configurations is to be used in a given cell, as described inmore detail above.

A non-synchronous PRACH signal is transmitted using a selected preamblestructure based on cell size when data is ready for transmission asdescribed above; in response, scheduling commands are received from theserving base station. Among the scheduling commands can be a command(implicit or explicit) to use a particular sub-channel for transmissionthat has been selected by the serving NodeB. Transmission of thescheduled resource blocks are performed by the transceiver using thesub-channel designated by the serving NodeB. Frequency hopping may beimplied by using two or more sub-channels as commanded by the servingNodeB. In this embodiment, a single transceiver supports OFDMA andSC-FDMA operation but other embodiments may use multiple transceiversfor different transmission standards. Other embodiments may havetransceivers for a later developed transmission standard withappropriate configuration. RF transceiver 1006 is connected to DBB 1002which provides processing of the frames of encoded data being receivedand transmitted by cell phone 1000.

The basic SC-FDMA DSP radio can include DFT, subcarrier mapping, andIFFT (fast implementation of IDFT) to form a data stream fortransmission and DFT, subcarrier de-mapping and IFFT to recover a datastream from a received signal, as described in more detail in FIGS. 6-7.DFT, IFFT and subcarrier mapping/de-mapping may be performed byinstructions stored in memory 1012 and executed by DBB 1002 in responseto signals received by transceiver 1006.

DBB unit 1002 may send or receive data to various devices connected toUSB (universal serial bus) port 1026. DBB 1002 is connected to SIM(subscriber identity module) card 1010 and stores and retrievesinformation used for making calls via the cellular system. DBB 1002 isalso connected to memory 1012 that augments the onboard memory and isused for various processing needs. DBB 1002 is connected to Bluetoothbaseband unit 1030 for wireless connection to a microphone 1032 a andheadset 1032 b for sending and receiving voice data.

DBB 1002 is also connected to display 1020 and sends information to itfor interaction with a user of cell phone 1000 during a call process.Display 1020 may also display pictures received from the cellularnetwork, from a local camera 1026, or from other sources such as USB1026.

DBB 1002 may also send a video stream to display 1020 that is receivedfrom various sources such as the cellular network via RF transceiver1006 or camera 1026. DBB 1002 may also send a video stream to anexternal video display unit via encoder 1022 over composite outputterminal 1024. Encoder 1022 provides encoding according toPAL/SECAM/NTSC video standards.

As used herein, the terms “applied,” “coupled,” “connected,” and“connection” mean electrically connected, including where additionalelements may be in the electrical connection path. “Associated” means acontrolling relationship, such as a memory resource that is controlledby an associated port. The terms assert, assertion, de-assert,de-assertion, negate and negation are used to avoid confusion whendealing with a mixture of active high and active low signals. Assert andassertion are used to indicate that a signal is rendered active, orlogically true. De-assert, de-assertion, negate, and negation are usedto indicate that a signal is rendered inactive, or logically false.

While the invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various other embodiments of the invention will beapparent to persons skilled in the art upon reference to thisdescription.

Embodiments of this invention apply to any flavor of frequency divisionmultiplex based transmission. Thus, the concept of valid specificationof sub-channels can easily be applied to: OFDMA, OFDM, DFT-spread OFDM,DFT-spread OFDMA, SC-OFDM, SC-OFDMA, MC-CDMA, and all other FDM-basedtransmission strategies.

A NodeB is generally a fixed station and may also be called a basetransceiver system (BTS), an access point, or some other terminology. AUE, also commonly referred to as terminal or mobile station, may befixed or mobile and may be a wireless device, a cellular phone, apersonal digital assistant (PDA), a wireless modem card, and so on.

In a general embodiment of the present disclosure, the set of allowedPRACH preamble signals is defined by two other sets: 1) a set of allowedroot CAZAC sequences, and 2) a set of allowed modifications to a givenroot CAZAC sequence. In one embodiment, PRACH preamble signal isconstructed from a CAZAC sequence, such as a ZC sequence. Additionalmodifications to the selected CAZAC sequence can be performed using anyof the following operations: multiplication by a complex constant, DFT,IDFT, FFT, IFFT, cyclic shifting, zero-padding, sequenceblock-repetition, sequence truncation, sequence cyclic-extension, andothers. Thus, in various embodiments of the present disclosure, a UEconstructs a PRACH preamble signal by selecting a CAZAC sequence,possibly applying a combination of the described modifications to theselected CAZAC sequence, modulating the modified sequence, andtransmitting the resulting PRACH signal over the air.

In some embodiments, the fixed set of preamble parameters stores boththe cyclic shift values and the number of root sequences, while in otherembodiments the cyclic shift values are stored and the number of rootsequences is computed from the cyclic shift values.

It is therefore contemplated that the appended claims will cover anysuch modifications of the embodiments as fall within the true scope andspirit of the invention.

What is claimed is:
 1. A method for transmitting a preamble, comprising:maintaining a fixed set of preamble parameter configurations; receivingat a user equipment (UE) a configuration number; selecting, with the UE,a preamble parameter configuration specified by the receivedconfiguration number from the fixed set of preamble parameterconfigurations; and transmitting, with the UE, a preamble using thepreamble parameter configuration indicated by the configuration number.2. The method of claim 1, wherein each preamble parameter configurationof the set of preamble parameter configurations implicitly defines anumber of root sequences and a number of cyclic shifts per rootsequence.
 3. The method of claim 2, wherein the fixed set of preambleparameter configurations comprises no more than sixteen preambleparameter configurations.
 4. The method of claim 2, wherein transmittinga preamble comprises: determining the number of root sequences and thenumber of cyclic shifts of the selected preamble parameterconfiguration; mapping a predetermined number of preamble signatures tosubsequent cyclic shifts of a given root sequence according to thenumber of cyclic shifts until the given root sequence is full, for allof the number of root sequences until a last root sequence; adjustingthe number of cyclic shifts mapped onto the last root sequence such thatthe predetermined number of preamble signatures are mapped; andselecting one of the mapped preamble signatures for use in transmittingthe preamble.
 5. The method of claim 4, wherein the predetermined numberof preamble signatures is sixty-four.
 6. The method of claim 1, whereinthe fixed set of preamble parameter configurations sample the continuouscell size range covered by a cellular network in a non-linear way, suchthat a finer configuration granularity is provided for smaller cells,whereby a broader deployment of smaller cells compared to larger cellsis better supported.
 7. A user equipment (UE), comprising: means forstoring a fixed set of preamble parameter configurations; means forreceiving information by the UE that designates a particular preambleparameter configuration from the fixed set of preamble parameterconfigurations; means for selecting a preamble parameter configurationspecified by the received configuration number from the fixed set ofpreamble parameter configurations; and means for transmitting a preamblefrom the UE using the preamble parameter configuration indicated by theconfiguration number.
 8. The UE of claim 7, wherein each preambleparameter configuration of the set of preamble parameter configurationsimplicitly defines a number of root sequences and a number of cyclicshifts per root sequence.
 9. The UE of claim 8, wherein the fixed set ofpreamble parameter configurations comprises no more than sixteenpreamble parameter configurations.
 10. The UE of claim 8, wherein themeans for transmitting a preamble comprises: means for determining thenumber of root sequences and the number of cyclic shifts of the selectedpreamble parameter configuration; means for mapping a predeterminednumber of preamble signatures to subsequent cyclic shifts of a givenroot sequence according to the number of cyclic shifts until the givenroot sequence is full, for all of the number of root sequences until alast root sequence; means for adjusting the number of cyclic shiftsmapped onto the last root sequence such that the predetermined number ofpreamble signatures are mapped; and means for selecting one of themapped preamble signatures for use in transmitting the preamble.
 11. Auser equipment (UE), comprising: a receiver operable to receiveinformation that designates a particular configuration number of a fixedset of preamble parameter configurations; a processor connected to astorage memory holding instructions for execution by the processor andfor holding the fixed set of preamble parameter configurations andconnected to obtain signals from the receiver, wherein the processor isoperable to select a preamble parameter configuration specified by thereceived configuration number from the fixed set of preamble parameterconfigurations; and a transmitter connected to the processor operable totransmit a signal from the cellular telephone UE using the selectedpreamble parameter configuration.
 12. The cellular telephone UE of claim11, wherein each preamble parameter configuration of the set of preambleparameter configurations implicitly defines a number of root sequencesand a number of cyclic shifts per root sequence.
 13. The cellulartelephone UE of claim 12, wherein the fixed set of preamble parameterconfigurations comprises no more than sixteen preamble parameterconfigurations.
 14. The cellular telephone UE of claim 12, wherein thetransmitter comprises: circuitry for determining the number of rootsequences and the number of cyclic shifts of the selected preambleparameter configuration; circuitry for mapping a predetermined number ofpreamble signatures to subsequent cyclic shifts of a given root sequenceaccording to the number of cyclic shifts until the given root sequenceis full, for all of the number of root sequences until a last rootsequence; circuitry for adjusting the number of cyclic shifts mappedonto the last root sequence such that the predetermined number ofpreamble signatures are mapped; and circuitry for selecting one of themapped preamble signatures for use in transmitting the preamble.